http://lpc.opengameart.org/
EDIT1: The liberated cup first phase has started.
Artists to your tablets and pencils, follow the style guide and win up to 1500 $ (US dollars).
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A two phases competition with a over 12k $ of funding that will be given into prizes.
The first phase is for artists, and is about making game assets.
The second phase is about making games with the assets of the first phase.
All assets and games are to be released under open sources formats.
The Liberated Pixel Cup is sponsored by Creative Commons, Mozilla, OpenGameArt, the Free Software Foundation, and people who donate(d).
You can check the complete rules for the competition.
As far as code goes, I don't know if games made in C2 can enter.
Releasing the exported code (so not minified on export) is "due" because of javascript's nature, but I don't know if it is a big deal/ok to release it in GPL.
And with C2, the "true" source code is the capx. I don't know if this wouldn't disqualify C2 entries as capx can only be "compiled" in the IDE in windows.
I guess if someone is interested in joining this competition, they should ask first and let us know <img src="smileys/smiley1.gif" border="0" align="middle">
For CC, unfortunately the rules disqualify any entry. The IDE is open source, but the end game is executed/compiled only on windows.
As for artists on the forum, I guess they can all enter.
It's also worth noting that a lot of assets might be produced for this competition and could be a valuable source in the future.